Method and apparatus for providing uninterruptible power

ABSTRACT

At least one aspect is directed to an uninterruptible power supply that includes a first input having an input line connection and an input neutral connection to receive a first input voltage from a first voltage source, a second input to receive a second input voltage from a second voltage source, and a boost circuit configured to provide a positive output DC voltage with respect to the input neutral connection and a negative output DC voltage with respect to the input neutral connection in both a line mode of operation and a backup mode of operation. The power supply also includes a first connection circuit to couple the first input to the boost circuit in the line mode of operation, and a second connection circuit to couple the second input to the boost circuit in the backup mode of operation, the second connection circuit being configured to isolate the second voltage source from the input neutral connection in the line mode of operation.

BACKGROUND OF INVENTION

1. Field of Invention

Embodiments of the invention relate generally to power supplies and morespecifically, at least one embodiment relates to a method and apparatusfor generating an output voltage derived from an input voltage.

2. Discussion of Related Art

Uninterruptible power supplies (UPS) for providing power to criticalloads are well known. FIG. 1 provides a block diagram of a typicalon-line UPS 100 that provides regulated power as well as back-up powerto a load 140. The UPS 100 includes a rectifier/boost converter 110, aninverter 120, a controller 130 and a battery 150. The UPS has inputs 112and 114 to couple respectively to line and neutral of an input AC powersource and has outputs 116 and 118 to provide an output line and neutralto the load 140.

In line mode of operation, under control of the controller, therectifier/boost converter 110 receives the input AC voltage and providespositive and negative output DC voltages at output lines 120 and 122with respect to a common or neutral line 124. In battery mode ofoperation, upon loss of input AC power, the rectifier/boost converter110 generates the DC voltages from the battery 150. The common line 124may be coupled to the input neutral 114 and the output neutral 118 toprovide a continuous neutral through the UPS 100. The inverter 120receives the DC voltages from the rectifier/boost converter 110 andprovides an output AC voltage at lines 116 and 118.

Further details of the rectifier/boost converter 110 and the battery 150are shown in FIGS. 2A and 2B with FIG. 2A showing the UPS in line modeof operation and FIG. 2B showing the UPS in battery mode of operation.The rectifier/boost converter 110 includes input diodes 160, 162, inputcapacitors 164, 166, relays 168 and 170, inductors 172 and 174, boosttransistors 176 and 178, diode 177, output diodes 180, 182, and outputcapacitors 184, 186. In addition, the rectifier/boost converter includesa transistor 188 that, as described below functions as part of abuck-boost circuit in the battery mode of operation.

In line mode of operation, relays 168, 170 are configured as shown inFIG. 2A to couple an input AC line voltage at inputs 112, 114 toinductors 172 and 174, such that positive and negative rectifiedvoltages are respectively provided to inductors 172 and 174. Inductor172 operates in conjunction with transistor 176 and diode 180 as apositive boost circuit under the control of the controller 130 usingpulse width modulation to provide a positive DC voltage across capacitor184. Similarly, inductor 174 operates in conjunction with transistor 178and diode 182 as a negative boost circuit under the control of thecontroller 130 using pulse width modulation to provide a negative DCvoltage across capacitor 186. The controller may control operation ofthe boost circuits to provide power factor correction at the input ofthe uninterruptible power supply, with the input currents beingsinusoidal with low total harmonic distortion and substantially in phasewith the input voltage.

In battery or backup mode of operation, for example, upon failure of theAC voltage source, the relays 168, 170 are moved, under the control ofthe controller, to the positions shown in FIG. 2B to couple the battery150 to inductors 172 and 174. In the battery mode of operation, thepositive boost circuit operates as discussed above using the batteryvoltage to generate the DC voltage across capacitor 184. To generate thenegative voltage across the capacitor 186 in battery mode, thetransistor 188, under the control of the controller, in conjunction withinductor 174 and diode 182 functions as a buck-boost circuit withtransistor 188 being cycled off and on. In one version, during eachcycle, transistor 178 is turned on immediately prior to transistor 188being turned on to reduce the voltage across transistor 188 at the timeof turn-on to approximately the battery voltage. The drive signal totransistor 178 remains on for the duration of the on time of transistor188. There is no current flow in transistor 178 due to the fact that theemitter of transistor 178 is at the battery voltage. When transistor 188is turned off, transistor 178 is again forward biased and the inductorcurrent flows through diode 177 and transistor 178. Transistor 178 stayson for 0.5 microseconds to allow transistor 188 to turn off totally, andis then turned off.

The UPS described above allows a single battery to be used in a dual DCbus (also referred to as a split DC bus) rectifier converter circuit.Other approaches utilize dual batteries or a split battery having amidpoint to generate the positive and negative bus voltages in batterymode of operation.

Another approach to using a single battery in a split DC bus rectifierconverter circuit is described in U.S. Pat. No. 6,661,678 to Raddi etal. The Raddi patent describes approaches in which either a relay or adiode circuit is used to couple a single battery to dual DC buses in aUPS.

SUMMARY OF INVENTION

At least one aspect of the invention is directed to an improveduninterruptible power supply and method for providing uninterruptiblepower. The uninterruptible power supply includes a first input having aninput line connection and an input neutral connection to receive a firstinput voltage from a first voltage source, a second input to receive asecond input voltage from a second voltage source, a boost circuitconfigured to provide a positive output DC voltage with respect to theinput neutral connection and a negative output DC voltage with respectto the input neutral connection in both a line mode of operation and abackup mode of operation, a first connection circuit to couple the firstinput to the boost circuit in the line mode of operation, and a secondconnection circuit to couple the second input to the boost circuit inthe backup mode of operation, wherein the uninterruptible power supplyis constructed and arranged to isolate the second voltage source fromthe input neutral connection in the line mode of operation.

In the uninterruptible power supply, the second voltage source may be abattery, and the uninterruptible power supply may include the battery.The uninterruptible power supply may include an output circuit coupledto the boost circuit to receive the positive output DC voltage and thenegative output DC voltage and to provide an output AC voltage at anoutput having an output line connection and an output neutralconnection. The uninterruptible power supply may be configured toprovide an uninterrupted connection from the input neutral connection tothe output neutral connection. The first connection circuit may includeat least one relay. The boost circuit may have a positive input, anegative input and a neutral input, wherein the neutral input is coupledto the input neutral connection, and wherein the second connectioncircuit includes a first diode coupled between a positive terminal ofthe battery and the positive input and a second diode coupled between anegative terminal of the battery and the negative input. Theuninterruptible power supply may further include a first relay coupledin parallel with the first diode and a second relay coupled in parallelwith the second diode. The uninterruptible power supply may beconfigured to operate with an AC voltage source at the first inputhaving a peak AC voltage that is less than the positive output DCvoltage, and the battery may have a battery voltage that is less thanthe positive output DC voltage. The uninterruptible power supply mayfurther include a battery charging circuit coupled to the battery, thebattery charging circuit having a positive charging circuit and anegative charging circuit, wherein the positive charging circuit isconfigured to charge the battery during a positive portion of the firstinput voltage, and wherein the negative charging circuit is configuredto charge the battery during a negative portion of the first inputvoltage. The uninterruptible power supply may be constructed andarranged to isolate the first voltage source from the boost circuit in abackup mode of operation and draw current from the second voltagesource. The power supply may be constructed and arranged tosimultaneously draw current from both the first voltage source and thesecond voltage source in a combined mode of operation.

A second aspect of the invention is also directed to an uninterruptiblepower supply the uninterruptible power supply includes a first inputhaving an input line connection and an input neutral connection toreceive a first input voltage from a first voltage source, a secondinput to receive a second input voltage from a second voltage source, aboost circuit configured to provide a positive output DC voltage withrespect to the input neutral connection and a negative output DC voltagewith respect to the input neutral connection in both a line mode ofoperation and a backup mode of operation, and means for coupling thesecond input to the boost circuit in the backup mode of operation andfor isolating the second voltage source from the input neutralconnection in the line mode of operation to prevent current flow fromthe second voltage source in the line mode of operation.

In the uninterruptible power supply, the second voltage source may be abattery, and the uninterruptible power supply may include the battery.The uninterruptible power supply may further include an output circuitcoupled to the boost circuit to receive the positive output DC voltageand the negative output DC voltage and to provide an output AC voltageat an output having an output line connection and an output neutralconnection. The uninterruptible power supply may be configured toprovide an uninterrupted connection from the input neutral connection tothe output neutral connection. The uninterruptible power supply mayfurther include means for isolating the boost circuit from the firstvoltage source in the backup mode of operation. In the uninterruptiblepower supply, the boost circuit may have a positive input, a negativeinput and a neutral input, wherein the neutral input is coupled to theinput neutral connection, and wherein the means for coupling includes afirst diode coupled between a positive terminal of the battery and thepositive input and a second diode coupled between a negative terminal ofthe battery and the negative input. The uninterruptible power supply mayfurther include a first relay coupled in parallel with the first diodeand a second relay coupled in parallel with the second diode. Theuninterruptible power supply may be configured to operate with an ACvoltage source at the first input having a peak AC voltage that is lessthan the positive output DC voltage, and the battery may have a batteryvoltage that is greater than the peak AC voltage and less than thepositive output DC voltage. The uninterruptible power supply may furtherinclude means for charging the battery, and means for simultaneouslydrawing current from both the first voltage source and the secondvoltage source in a combined mode of operation.

Another aspect of the invention is directed to a method of providingpower to a load. The method includes receiving input power at a lineconnection and a neutral connection from a first voltage source,rectifying the input power to produce a first rectified voltage at afirst node during a positive portion of an input voltage wave and asecond rectified voltage at a second node during a negative portion ofthe input voltage wave, in a line mode of operation, producing apositive DC voltage with respect to the neutral connection from thefirst rectified voltage and a negative DC voltage with respect to theneutral connection from the second rectified voltage, coupling a secondvoltage source to the first node and the second node using a connectioncircuit that is configured to isolate the second voltage source from theneutral connection in the line mode of operation.

The second voltage source may be a battery, and the method may furtherinclude detecting an outage of the first voltage source, and producingthe positive DC voltage and the negative DC voltage from a voltage ofthe battery in a backup mode of operation. The method may furtherinclude producing an output AC voltage from the positive DC voltage andthe negative DC voltage in both the line mode of operation and thebackup mode of operation. The method may further include isolating thefirst voltage source from the first node and the second node in thebackup mode of operation. The method may further include simultaneouslydrawing current from both the first voltage source and the secondvoltage source in a combined mode of operation.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures is represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1 is a functional block diagram of an uninterruptible power supply;

FIG. 2A is a schematic diagram of a prior art rectifier/boost converterthat may be used in the uninterruptible power supply of FIG. 1 with therectifier/boost converter in a first state of operation;

FIG. 2B is a schematic diagram of the rectifier/boost converter of FIG.2A in a second state of operation;

FIG. 3A is a schematic diagram of a rectifier/boost circuit inaccordance with one embodiment of the invention;

FIGS. 3B-3I are schematic diagrams indicating current paths in differentmodes of operation of the rectifier/boost circuit of FIG. 3A;

FIG. 4 is a schematic diagram of a rectifier/boost circuit in accordancewith another embodiment of the invention;

FIG. 5 is a schematic diagram of a rectifier/boost circuit in accordancewith yet another embodiment of the invention.

FIGS. 6A and 6B are schematic diagrams indicating current paths using analternative control scheme in a battery mode of operation of therectifier/boost circuit of FIG. 3A; and

FIGS. 7A-7D are schematic diagrams indicating current paths during analternative mode of operation of the rectifier/boost circuit of FIG. 3A.

FIG. 8 shows a waveform of current draw in one embodiment.

DETAILED DESCRIPTION

This invention is not limited in its application to the details ofconstruction and the arrangement of components set forth in thefollowing description or illustrated in the drawings. The invention iscapable of other embodiments and of being practiced or of being carriedout in various ways. Also, the phraseology and terminology used hereinis for the purpose of description and should not be regarded aslimiting. The use of “including,” “comprising,” or “having,”“containing”, “involving”, and variations thereof herein, is meant toencompass the items listed thereafter and equivalents thereof as well asadditional items.

As discussed above, prior approaches have provided for the use of asingle battery in a split DC bus UPS. There are some drawbacks with theapproaches discussed above. First, the use of relays or SCR's betweenthe battery and the boost circuits typically requires that the DC buscapacitors have increased capacitance to maintain the bus voltagesduring switching of the SCR's upon loss of line power. Second, the SCR'srequire the use of gate circuits adding to the complexity and the costof the UPS. In circuits using diodes, such as in U.S. Pat. No. 6,661,678described above, the power factor correction circuit is typicallydisabled when the absolute value of the positive or negativeinstantaneous AC voltage is less than the battery voltage to preventcurrent from being drawn from the battery in line mode of operation.Because current is not drawn throughout the entire AC voltage waveform,the ability to provide an input current with very low total harmonicdistortion is limited. This lowers the possible obtainable power factor.To help alleviate this problem, it is possible to use a battery of lowervoltage, but the use of a lower voltage battery results in highercurrent draws resulting in the need to use higher rated, more expensivecomponents. Still further, in at least some solutions of the prior art,in battery mode of operation, series diodes are used between at leastone of the boost transistors and the neutral in the primary batterycurrent path. These diodes have associated losses that reduce theefficiency of the uninterruptible power supply system.

As will now be described, in at least one embodiment of the presentinvention, a rectifier/boost converter circuit 210 that may be used, forexample, in a UPS, such as that shown in FIG. 1, is configured toinclude an improved battery connection circuit to overcome at least oneof the drawbacks discussed above. The rectifier/boost circuit 210 isshown in FIG. 3A coupled to an AC power source 201 through a relay 203.The rectifier/boost circuit 210 includes input diodes 260, 262, inputcapacitors 264, 266, battery connection diodes 268, 270, inductors 272,274, boost transistors 276 and 278, output diodes 280, 282, and outputcapacitors 284, 286. In addition, the rectifier/boost circuit includescapacitors 252, 253 and 254 that along with diodes 268 and 270 form abattery connection circuit to couple the battery 250 to the boosttransistors in battery mode of operation of rectifier/boost circuit 210.Capacitors 252, 253 and 254 may not be used in all embodiments, andprimarily are used to reduce electromagnetic interference on batterywires and to reduce ripple current in the battery.

The rectifier/boost circuit also includes positive and negative batterycharging circuits that charge the battery from power drawn from theoutput DC busses in line mode of operation. The positive batterycharging circuit includes an inductor 291, a diode 292 and a transistor293. The negative battery charging circuit includes an inductor 294, adiode 295 and a transistor 296. The rectifier/boost circuit may includecurrent and voltage sensing circuits to detect operationalcharacteristics of the rectifier/boost circuit to assist in control ofthe circuit by a controller, such as controller 130 shown in FIG. 1.

The rectifier/boost circuit 210 of FIG. 3A is similar to therectifier/boost circuit 110 shown in FIGS. 2A and 2B with a fewexceptions. First, while the circuit 110 uses relays to couple thebattery to the circuit in battery mode of operation, the circuit 110uses diodes 268 and 270 in a manner described below. Second, in thecircuit 110, the battery 150 has its negative terminal coupled to theneutral bus, while in circuit 210 there is no direct connection betweenthe neutral bus and the battery 250. Finally, the battery chargingcircuit is shown for the circuit 210 while the battery charging circuitfor the circuit 110 is not shown.

In line mode of operation, the relay 203 is in a closed position tocouple the AC line voltage from the AC voltage source 201 to the boostinductors 272 and 274 through diodes 260 and 262, such that positive andnegative rectified voltages are respectively provided to inductors 272and 274. During periods of positive AC voltage of the AC voltage source,inductor 272 operates in conjunction with transistor 276 and diode 280as a positive boost circuit under the control of a controller, such ascontroller 130, using pulse width modulation to provide a positive DCvoltage at the positive DC bus 120 across capacitor 284. Similarly,inductor 274 operates in conjunction with transistor 278 and diode 282as a negative boost circuit under the control of the controller usingpulse width modulation to provide a negative DC voltage at the negativeDC bus 122 across capacitor 286.

In the positive half cycle of the line voltage, transistor 278 remainsoff and during the negative half cycle of the line voltage, transistor276 remains off. With the battery voltage selected appropriately, thisensures that no voltage will be drawn from the battery during line modeof operation as there will be no current path to the negative terminalof the battery. The battery voltage in one embodiment is selected to belower than the bus voltage across each of the capacitors 284 and 286, toprevent current flow from the battery through diode 282, inductor 274and diode 270, which might otherwise occur during the positive portionof the input AC voltage. In the positive half cycle of the line voltage,the potential of the battery will float in a negative direction untilits positive terminal is at a voltage level below the instantaneousvalue of the AC line voltage, so that all input current to the positiveboost circuit is drawn from the AC voltage source through diode 260rather than from the battery through diode 268.

Operation in line mode will be further described with reference to FIGS.3B-3E. FIGS. 3B and 3C show an equivalent circuit for therectifier/boost circuit 210 in line mode of operation, during thepositive half cycle of the input voltage waveform. As shown in FIG. 3B,transistor 276 is first closed to create a current path 261 from the ACsource through diode 260, inductor 272, and transistor 276. Then, asshown in FIG. 3C, transistor 276 is opened, and capacitor 284 is chargedthrough a current path 263 that includes the AC source, diode 260,inductor 272, diode 280 and capacitor 284. As understood by thoseskilled in the art, during the positive half cycle, operation of thecircuit 210 alternates between the modes shown in FIGS. 3B and 3C tomaintain the voltage across capacitor 284 at a predetermined level.

Similarly, FIGS. 3D and 3E show current paths 365 and 367 in line modeof operation during negative half cycles of the input AC voltage. First,as shown in FIG. 3D, transistor 278 is closed to create a current path365 from the AC source through transistor 278, inductor 274 and diode262, and next, as shown in FIG. 3E, transistor 278 is opened and thecurrent follows a path 367 through capacitor 286, diode 282, inductor274 and diode 262.

The rectifier/boost circuit 210 switches from line mode of operation tobattery mode of operation when an out of tolerance condition (such asloss of power) of the AC voltage source occurs, and the relay 203 isswitched under control of the controller from the closed position to theopen position. The open position of the relay 203 is shown in FIG. 3A.In battery mode of operation, the control of the positive and negativeboost converter circuits is changed to a mode that allows power to bedrawn from the battery to create the positive and negative bus voltages.As described below, in different embodiments of the invention, differentcontrol schemes may be used to control the draw of power from thebattery in battery mode of operation.

In a first scheme, in which the rectifier/boost circuit is used in a UPShaving an output inverter like that described above with reference toFIG. 1, the draw of power from the battery in battery mode issynchronized with the output AC voltage waveform from the inverter, suchthat for the positive portion of the output AC waveform, the positiveboost converter circuit is used to develop voltage across capacitor 284,and for the negative portion of the output AC waveform, the negativeboost converter circuit is used to develop voltage across capacitor 286.More specifically, during the positive portion of the output waveform, apulse width modulated control signal is applied to transistor 276 togenerate the positive bus DC voltage across capacitor 284. During thepositive portion, the negative boost transistor 278 is kept continuouslyon to provide a current path from the neutral line to the negativeterminal of the battery through transistor 278, inductor 274 and diode270. FIGS. 3F and 3G show equivalent circuits with current paths 369 and371 during battery mode of operation for the positive portion of theoutput waveform. First, as shown in FIG. 3F, transistor 276 is closedcreating a current path 369 from the battery through diode 260, inductor272, transistors 276 and 278, inductor 274 and diode 262. Next, as shownin FIG. 3F, transistor 276 is opened and current takes a path 371 fromthe battery through inductor 272, diode 280, capacitor 284, transistor278, inductor 274, and diode 262.

In a similar manner, during the negative portion of the output waveform,a pulse width modulated control signal is applied to transistor 278 togenerate the negative DC voltage across capacitor 286. During thenegative portion, the positive boost transistor 276 is kept continuouslyon to provide a current path between the neutral line and the positiveterminal of the battery through transistor 276, inductor 272 and diode268. FIGS. 3H and 3I show equivalent circuits with current paths 373 and375 during battery mode of operation for the positive portion of theoutput waveform. First, as shown in FIG. 3H, transistor 278 is closedcreating a current path 373 from the battery through diode 268, inductor272, transistors 276 and 278, inductor 274 and diode 262. Next, as shownin FIG. 3I, transistor 276 is opened and current takes a path 375 fromthe battery through inductor 272, transistor 277, capacitor 286, diode282, inductor 274, and diode 262.

In at least one embodiment, precautions may be taken to reduceundesirable high peak currents through transistors 276 and 278 as theyare switched to the continuously on state in battery mode of operation.The high peak currents may occur due to discharging of capacitors 253,254, 264 and 266 when the transistors are turned continuously on. Morespecifically, when transistor 278 is turned continuously on, capacitor254 may be discharged through transistor 278, inductor 274 and diode270. Also capacitor 266 may be discharged through transistor 278, andinductor 274. In a similar manner, capacitors 253 and 264 may bedischarged through transistor 276 when transistor 276 is turnedcontinuously on.

In one embodiment to prevent the high peak current, transistors 276 and278 may be controlled by the controller to limit the current flowthrough the transistors. The current may be limited by implementingcurrent control circuits with each of the transistors, or alternativelyusing digital control in the controller 130. The current controlcircuits (or controller) vary the pulse width modulation signals to thetransistors (when in the PWM mode) such that the current in theassociated inductor (inductor 272 for transistor 276 and inductor 274for transistor 278) follow a reference current signal. The current inthe non-PWM transistor can then be controlled to limit the current to avalue that is somewhat higher than that of the reference current signalto limit the amount of current through the transistor due to dischargeof one of the capacitors.

In another embodiment, to limit current during battery mode of operationin the boost inductors and transistors, additional transistors may beadded across each of capacitors 253 and 254. A rectifier/boost circuit310 having the added transistors 298 and 299 is shown in FIG. 4. Therectifier boost/circuit 310 is substantially similar to rectifier/boostcircuit 210 with the exception that in the circuit 310, the transistors298 and 299 and associated anti-parallel diodes 301 and 303 have beenadded across respectively capacitors 253 and 254. Circuit 310 operatesin a manner similar to circuit 210 described above with the exceptionthat each of transistors 298 and 299 is controlled in battery mode ofoperation to turn on when the voltage across its associated capacitor(253 or 254) is discharged to zero. The anti-parallel diodes 301 and 303are used to ensure that transistors 298 and 299 do not have a negativevoltage across them. Such a negative voltage could be harmful, when, forexample, the transistors are implemented using IGBT's. The anti-paralleldiodes may be implemented using the internal body diode of itsassociated transistor when MOSFET transistors are used, or they may beimplemented using a co-packed device that includes a diode.

More specifically, in battery mode of operation, as discussed above,during the positive portion of the output AC waveform, the positiveboost circuit (inductor 272, transistor 276 and diode 280) is controlledin a pulse width mode of operation, and transistor 278 remains on toprovide a current return path to the negative terminal of the battery.In the embodiment shown in FIG. 4, after capacitor 254 is discharged toa voltage close to zero (due to transistor 278 being on) transistor 299is turned on. The return path for the current through the positive boostcircuit is then through transistor 299, thereby limiting the total rmscurrent through transistor 278, inductor 274 and diode 270 during thepositive half-cycle of the output voltage waveform. Similarly, duringthe negative half-cycle of the output voltage waveform, when thenegative boost circuit (inductor 274, transistor 278 and diode 282) isoperating in pulse width mode, transistor 298 is turned on oncecapacitor 253 is discharged to a voltage close to zero. In anothercontrol scheme used with the embodiment shown in FIG. 4, each oftransistors 298 and 299 may be turned on at the same time that itscorresponding boost transistor 276 and 278 is turned on to discharge thecapacitors. In another scheme, the battery charging circuit (which isdescribed in further detail below) is operated as a bidirectional powerconverter to discharge the capacitors 253 and 254 while further chargingone of capacitors 284 and 286.

In another embodiment, a rectifier/boost circuit 410 includes relays 411and 412 that may be used to lower losses of the circuit when operatingin battery mode of operation. The rectifier/boost circuit having theadded relays 411 and 412 is shown in FIG. 5. The rectifier/boost circuit410 is substantially similar to rectifier boost circuits 210 and 310described above with the exception that in the circuit 410, the relays411 and 412 have been added respectively across diodes 268 and 270. Thecircuit 410 includes transistors 298 and 299, however, in otherembodiments, these transistors do not need to be included. Circuit 410operates in a manner similar to circuits 210 and 310 described abovewith the exception that when entering battery mode, shortly after theopening of relay 203, each of relays 411 and 412 is controlled to closeunder the control of the controller. The closing of the relays duringbattery mode of operation avoids sustained conduction losses in diodes268 and 270. In one embodiment, during operation of the circuit 410 inbattery mode, upon return of line power, the relays 411 and 412 areopened prior to the closing of relay 203. The relays 411 and 412 may beimplemented using individual relays or in one embodiment may beimplemented using a common two-pole relay with a first set of contactsof the relay coupled across diode 268 and a second set of contacts ofthe relay coupled across diode 270.

As will now be described, in another embodiment, a different controlscheme is provided for controlling the operation of the rectifier boostcircuit 210 in battery mode of operation. In general, in thisembodiment, both transistors 276 and 278 are constantly switching andthere is a substantially constant power flow to each of the buscapacitors 284, 286. Current paths in this control scheme will now bedescribed with reference to FIGS. 6A and 6B. As shown in FIG. 6A, in afirst stage of operation in battery mode, current follows path 377through diode 268, inductor 272, transistor 276, transistor 278,inductor 274, and diode 262. Next, in a second stage of operation asshown in FIG. 6B, current follows a path 379 to charge capacitors 284and 286. Current path 377 starts with the battery 250 and goes throughdiode 268, inductor 272, diode 280, capacitors 284 and 286, diode 282,inductor 274 and diode 262.

One advantage of the second control scheme is that the battery will stayat a relatively constant voltage level, so there is no need to considerspecial precautions with regard to the discharging of capacitors 253 and254. The first control scheme can be beneficial by having switchinglosses in each of the boost transistors 276, 278 during only half of theoperational time. For embodiments employing the second control scheme,the transistors 298 and 299 are not used, however, the relays 411 and412 can be used to reduce conduction losses in the diodes.

As briefly discussed above, transistors 293, 296, diodes 292, 295 andinductors 291 and 294 are used in a charging circuit to charge thebattery 250 in line mode of operation of the rectifier/boost circuit210. More specifically, inductor 291, diode 292 and transistor 293 areused to implement a positive charging circuit and inductor 294, diode295 and transistor 296 are used to implement a negative chargingcircuit. Each of the positive and negative charging circuits arecontrolled as buck converters to provide a regulated voltage across thebattery. During the positive half cycle of the line voltage, thenegative charging circuit is used to charge the battery 250. Thetransistor 296 is switched on and off under control of the controllerusing pulse width modulation to provide a controlled current and voltageto the battery. When the transistor 296 is on, current flows through apath that includes diode 292, inductor 291, battery 250, inductor 294and transistor 296. When the transistor is turned off, inductors 291 and294 discharge through the battery in a path that includes inductor 291,battery 250, inductor 294, diode 295 and diode 292.

In a similar manner, during the negative half cycle of the line voltage,the positive charging circuit is used to charge the battery 250. Thetransistor 293 is switched on and off under the control of thecontroller using pulse width modulation to provide a controlled currentand voltage to the battery. When the transistor 293 is on, current flowsthrough a path that includes transistor 293, inductor 291, battery 250,inductor 294 and diode 295. When the transistor is turned off, inductors291 and 294 discharge through the battery in a path that includesinductor 291, battery 250, inductor 294, diode 295 and diode 292.

A particular advantage of the charging circuitry described above is thatdual charging circuits are provided to allow charging of the batteryduring both the positive and negative half cycles of the input ACvoltage waveform. In addition, in the dual charging circuits the use ofthe same two inductors in both the positive and negative chargingcircuits allows the size of each inductor to be reduced.

In other embodiments, other types of charging circuits may be used, forexample, a transformer-coupled switched mode power converter may used.In such an embodiment, the converter can be coupled directly across thebattery as the transformer provides galvanic isolation that allows thecharging circuit to effectively charge the battery even though thebattery potential is moving with respect to the neutral during line modeof operation.

In another embodiment, boost/rectifier circuits described above arecontrolled to simultaneously draw power from both line and battery. Thewaveform drawn from the line may be controlled to be sinusoidal toobtain substantially uniform power factor, and the current drawn fromthe battery may at the same time be substantially ripple-free DCcurrent. In at least one version, the amount of power drawn from lineand from battery can be controlled individually, so that the total powerinput can be any fractional mix of power from the two sources.

The ability to draw power from both sources provides a number ofbenefits. First, in transferring from battery operation to lineoperation, a smooth transition can be used where line current isincreased gradually from zero to full current over a specific period ofmany line cycles. The gradual transfer can help to reduce or eliminatesurges in current. Such surges in current may cause unstable voltage orfrequency from the source, particularly if the source is a dieselgenerator or equivalent.

Another benefit of the simultaneous power draw is that battery currentcan be used to supplement line current during a temporary overload toavoid tripping of an AC circuit breaker or fuse. In one version, whenline current exceeds a given value, a UPS containing embodiments of theinvention are controlled to simultaneously draw current from the batteryand from the AC line to limit the current draw from the line source.

Still another benefit of simultaneous power draw is that during low linevoltage scenarios a UPS can be controlled to draw battery current aswell as line current to prevent current overloads, while allowing somepower to be drawn from the AC line to prevent rapid discharging ofbatteries.

In one embodiment, to achieve simultaneous power draw, in respectivelypositive and negative half cycles, one of the two boost circuits of theboost rectifier 210 is controlled to draw current with a waveform thatincludes an AC portion (from a line source) and a DC portion (frombattery), while the opposite booster is controlled to draw only a DCportion (from battery). Ideally, the DC portions are equal. In at leastone version, the battery charger is turned off during simultaneouscurrent draw, with components 291, 292, 293, 294, 295 and 296 off.

Current paths in the boost rectifier circuit 210 for simultaneous powerdraw from battery and a line source will now be described with referenceto FIGS. 7A-7D. As in the embodiments described above, transistors 276and 278 are turned on and off using pulse width modulation control toregulate the voltage across bus capacitors 284 and 286. FIG. 7A shows afirst AC current path 381 (with dashed lines) and a first DC currentpath 383 (with solid lines) for simultaneous operation for a positiveportion of the input AC waveform with transistors 276 and 278 closed. Inthis mode, AC current follows a path 381 from the AC source throughdiode 260, inductor 272, transistor 276 and back to the AC source. Inthis mode DC current follows a path 383 from the battery through diode268, inductor 272, transistor 276, transistor 278, inductor 274, anddiode 270. FIG. 7B shows a second AC current path 385 (with dashedlines) and a second DC current path 387 (solid lines) for simultaneousoperation for the positive portion of the input AC waveform withtransistors 276 and 278 opened. In this mode, AC current follows a path385 from the AC source through diode 260, inductor 272, diode 280,capacitor 284 and back to the AC source. In this mode DC current followsa path 387 from the battery through diode 268, inductor 272, diode 280,capacitor 284, capacitor 286, diode 282, inductor 274, and diode 270.

FIGS. 7C and 7D show current paths for simultaneous operation for thenegative portion of the input AC voltage waveform. FIG. 7C shows a firstAC current path 389 (with dashed lines) and a first DC current path 391(with solid lines) for simultaneous operation for the negative portionof the input AC waveform with transistors 276 and 278 closed. In thismode, AC current follows a path 389 from the AC source throughtransistor 278, inductor 274, diode 262 and back to the AC source. Inthis mode DC current follows a path 391 (which is the same as path 383)from the battery through diode 268, inductor 272, transistor 276,transistor 278, inductor 274, and diode 270. FIG. 7D shows a second ACcurrent path 393 (with dashed lines) and a second DC current path 395(solid lines) for simultaneous operation for the positive portion of theinput AC waveform with transistors 276 and 278 opened. In this mode, ACcurrent follows a path 393 from the AC source through capacitor 286,diode 282, inductor 274, diode 262, and back to the AC source. In thismode DC current follows a path 395 (which is the same as path 387) fromthe battery through diode 268, inductor 272, diode 280, capacitor 284,capacitor 286, diode 282, inductor 274, and diode 270.

In the operation described above, during positive half cycles of theinput voltage waveform, all current drawn by the negative boost circuitis provided by the battery as diode 262 will be blocked by the positiveline voltage. Similarly, during negative half-cycles, all current forthe positive boost circuit is provided by the battery as diode 260 willbe blocked by the negative line voltage. During the positive half cycle,the negative boost circuit controls the DC current being drawn, and thepositive boost circuit will draw additional AC current as necessaryabove the DC current. Similarly, during the negative half cycle, thepositive boost circuit controls the DC current being drawn, and thenegative boost circuit will draw additional AC current as necessaryabove the DC current.

FIG. 8 shows a waveform 510 of current draw by the boost/rectifiercircuit 210 for a transition from battery mode to line mode of operationusing simultaneous current draw from the battery and a line source. Inthe waveform 510, current through the positive boost circuit is shownwith a bolder line 512 and current through the negative boost circuit isshown with a finer line 514. During the time period from t0 to t1 inFIG. 8, the boost/rectifier circuit is drawing current from the batteryonly, during the time period t1 to t2, the boost rectifier circuit isdrawing current from both the battery and the AC line, and after timet2, the boost rectifier is drawing current from the AC line only. Asindicated by the waveform shown in FIG. 8, the use of simultaneouscurrent draw from two sources provides a smooth transition between thesources. In embodiments described above control techniques forsimultaneous current draw have been described for use with boostrectifier circuit 210. As readily understood by those skilled in the artgiven the benefit of this disclosure, other embodiments of UPS's andboost rectifiers described herein may be similarly controlled forsimultaneous current draw from multiple sources.

In embodiments described above, certain circuit components are describedas performing certain functions. As readily understood by one of skillin the art, other components or devices may be used to perform the sameor similar functions. In particular, relays used in certain embodimentsmay be implemented by a number of different devices that may be used asswitches, including traditional relays, transistors, SCR's and otherswitching devices. In certain embodiments, transistors are used asswitches, for example, in boost circuits. The transistors may beimplemented using, for example, IGBTs, MOSFETs, bipolar junctiontransistors or other devices readily known to those of skill in the artgiven the benefit of this disclosure.

Table 1 provides specific devices used to implement various componentsin at least one embodiment of the invention.

TABLE 1 ELECTRICAL COMPONENTS Reference Device No. Name Value Man/PartNo. 203 Relay 20 A Various 260 Diode 20 A/1200 V InternationalRectifier/ 20ETS12 262 Diode 20 A/1200 V International Rectifier/20ETS12 264 Capacitor 5 uF/250 Vac Various 266 Capacitor 5 uF/250 VacVarious 250 Battery 192 V (16 × 12 V) Various 252 Capacitor 1000 uF/250V Various 253 Capacitor 1 uF/250 V Various 254 Capacitor 1 uF/250 VVarious 268 Diode 20 A/800 V International Rectifier/ 20ETS08 270 Diode20 A/800 V International Rectifier/ 20ETS08 272 Inductor 500 uH/15 A RMSVarious 274 Inductor 500 uH/15 A RMS Various 280 Diode 15 A/600 Vultra-fast International Rectifier/ 15ETX06 282 Diode 15 A/600 Vultra-fast International Rectifier/ 15ETX06 276 Transistor 30 A/600 VInfineon/ SPW47N60C3 278 Transistor 30 A/600 V Infineon/ SPW47N60C3 284Capacitor 4700 uF/450 V Various 286 Capacitor 4700 uF/450 V Various 291Inductor 2.5 mH/1 A RMS Various 294 Inductor 2.5 mH/1 A RMS Various 292Diode 4 A/600 V ultra-fast International Rectifier/ HFA04TB60 295 Diode4 A/600 V ultra-fast International Rectifier/ HFA04TB60 293 Transistor4.5 A/600 V Infineon/ SPP04N60C3 296 Transistor 4.5 A/600 V Infineon/SPP04N60C3 298 Transistor 20 A/600 V Infineon/ IKP20N60T 299 Transistor20 A/600 V Infineon/ IKP20N60T 411 Relay 20 A Various 412 Relay 20 AVarious

As discussed above, embodiments of the present invention provide severaladvantages over prior solutions. In particular, at least one embodimentprovides for a dual bus UPS having a single battery that is able to drawa sinusoidal current and provide a power factor approaching unity. Inaddition, the single battery of at least one embodiment can generallyhave a greater voltage than in solutions of the prior art, since thebattery will not conduct during line mode of operation. At least oneembodiment may utilize a battery (or other backup power source) having avoltage that can approach the voltage of one side of the output DC bus.The use of a battery having a higher voltage results in lower batterycurrent allowing lower rated (and lower cost) transistors and inductorsto be used. In addition, in comparison with at least some priorsolutions, in at least one embodiment of the present invention, lossesare reduced as there are no diodes disposed between boost transistorsand the neutral of the power supply. Further, in comparison with priorsolutions that utilize switching circuits between the battery and theboost circuitry, at least one embodiment of the present inventionutilizes simple diodes between a battery and boost circuitry resultingin a simpler, faster, and lower-cost solution.

In embodiments described above, a battery is used as a backup powersource. In other embodiments, other AC or DC backup sources and devicesmay be used including solar powered devices, fuel cells, capacitors, asecondary AC power source, or any other power sources.

In embodiments described above, rectifier/boost circuits are describedfor use with uninterruptible power supplies. In other embodiments, therectifier/boost circuits may be used with other power supplies andelectronic devices.

In embodiments described above, output voltages are described as beingprovided at output DC busses. As readily understood by those skilled inthe art, the terms bus, busses and voltage rails are not limited toparticular types of conductors or wires to provide output voltages andmay include any one of a number of devices or components.

Embodiments of the present invention may be used with uninterruptiblepower sources having a variety of input and output voltages and may beused in single phase or multiphase uninterruptible power supplies.

In embodiments of the invention that utilize a battery as a backup powersource, the battery may be comprised of multiple batteries of cellscoupled in parallel or in series.

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated various alterations, modifications,and improvements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the spirit and scope ofthe invention. Accordingly, the foregoing description and drawings areby way of example only.

1. An uninterruptible power supply comprising: a first input having aninput line connection and an input neutral connection to receive a firstinput voltage from a first voltage source; a second input to receive asecond input voltage from a second voltage source; a boost circuitconfigured to provide a positive output DC voltage with respect to theinput neutral connection and a negative output DC voltage with respectto the input neutral connection in both a line mode of operation and abackup mode of operation; a first connection circuit to couple the firstinput to the boost circuit in the line mode of operation; and a secondconnection circuit to couple the second input to the boost circuit inthe backup mode of operation; wherein the uninterruptible power supplyis constructed and arranged to isolate the second voltage source fromthe input neutral connection in the line mode of operation.
 2. Theuninterruptible power supply of claim 1, wherein the second voltagesource is a battery, and wherein the uninterruptible power supplyincludes the battery.
 3. The uninterruptible power supply of claim 2,further comprising an output circuit coupled to the boost circuit toreceive the positive output DC voltage and the negative output DCvoltage and to provide an output AC voltage at an output having anoutput line connection and an output neutral connection.
 4. Theuninterruptible power supply of claim 3, wherein the uninterruptiblepower supply is configured to provide an uninterrupted connection fromthe input neutral connection to the output neutral connection.
 5. Theuninterruptible power supply of claim 1, wherein the first connectioncircuit includes at least one relay.
 6. The uninterruptible power supplyof claim 2, wherein the boost circuit has a positive input, a negativeinput and a neutral input, wherein the neutral input is coupled to theinput neutral connection, and wherein the second connection circuitincludes a first diode coupled between a positive terminal of thebattery and the positive input and a second diode coupled between anegative terminal of the battery and the negative input.
 7. Theuninterruptible power supply of claim 6, further comprising a firstrelay coupled in parallel with the first diode and a second relaycoupled in parallel with the second diode.
 8. The uninterruptible powersupply of claim 2, wherein the uninterruptible power supply isconfigured to operate with an AC voltage source at the first inputhaving a peak AC voltage that is less than the positive output DCvoltage, and wherein the battery has a battery voltage that is less thanthe positive output DC voltage.
 9. The uninterruptible power supply ofclaim 8, wherein the battery voltage is greater than the peak ACvoltage.
 10. The uninterruptible power supply of claim 2, furthercomprising a battery charging circuit coupled to the battery, thebattery charging circuit having a positive charging circuit and anegative charging circuit, wherein the positive charging circuit isconfigured to charge the battery during a positive portion of the firstinput voltage, and wherein the negative charging circuit is configuredto charge the battery during a negative portion of the first inputvoltage.
 11. The uninterruptible power supply of claim 1, wherein theuninterruptible power supply is constructed and arranged to isolate thefirst voltage source from the boost circuit in the backup mode ofoperation and draw current from the second voltage source.
 12. Theuninterruptible power supply of claim 11, wherein the power supply isconstructed and arranged to simultaneously draw current from both thefirst voltage source and the second voltage source in a combined mode ofoperation.
 13. The uninterruptible power supply of claim 12, wherein thesecond voltage source is a battery.
 14. An uninterruptible power supplycomprising: a first input having an input line connection and an inputneutral connection to receive a first input voltage from a first voltagesource; a second input to receive a second input voltage from a secondvoltage source; a boost circuit configured to provide a positive outputDC voltage with respect to the input neutral connection and a negativeoutput DC voltage with respect to the input neutral connection in both aline mode of operation and a backup mode of operation; and means forcoupling the second input to the boost circuit in the backup mode ofoperation and for isolating the second voltage source from the inputneutral connection in the line mode of operation.
 15. Theuninterruptible power supply of claim 14, wherein the second voltagesource is a battery, and wherein the uninterruptible power supplyincludes the battery.
 16. The uninterruptible power supply of claim 15,further comprising an output circuit coupled to the boost circuit toreceive the positive output DC voltage and the negative output DCvoltage and to provide an output AC voltage at an output having anoutput line connection and an output neutral connection.
 17. Theuninterruptible power supply of claim 16, wherein the uninterruptiblepower supply is configured to provided an uninterrupted connection fromthe input neutral connection to the output neutral connection.
 18. Theuninterruptible power supply of claim 14, further comprising means forisolating the boost circuit from the first voltage source in the backupmode of operation.
 19. The uninterruptible power supply of claim 15,wherein the boost circuit has a positive input, a negative input and aneutral input, wherein the neutral input is coupled to the input neutralconnection, and wherein the means for coupling includes a first diodecoupled between a positive terminal of the battery and the positiveinput and a second diode coupled between a negative terminal of thebattery and the negative input.
 20. The uninterruptible power supply ofclaim 19, further comprising a first relay coupled in parallel with thefirst diode and a second relay coupled in parallel with the seconddiode.
 21. The uninterruptible power supply of claim 15, wherein theuninterruptible power supply is configured to operate with an AC voltagesource at the first input having a peak AC voltage that is less than thepositive output DC voltage, and wherein the battery has a batteryvoltage that is less than the positive output DC voltage.
 22. Theuninterruptible power supply of claim 21, wherein the battery voltage isgreater than the peak AC voltage.
 23. The uninterruptible power supplyof claim 15, further comprising means for charging the battery.
 24. Theuninterruptible power supply of claim 14, further comprising means forsimultaneously drawing current from both the first voltage source andthe second voltage source in a combined mode of operation.
 25. Theuninterruptible power supply of claim 24, wherein the second voltagesource is a battery.
 26. A method of providing power to a load, themethod comprising: receiving input power at a line connection and aneutral connection from a first voltage source; rectifying the inputpower to produce a first rectified voltage at a first node during apositive portion of an input voltage wave and a second rectified voltageat a second node during a negative portion of the input voltage wave; ina line mode of operation, producing a positive DC voltage with respectto the neutral connection from the first rectified voltage and anegative DC voltage with respect to the neutral connection from thesecond rectified voltage; coupling a second voltage source to the firstnode and the second node using a connection circuit that is configuredto isolate the second voltage source from the neutral connection in theline mode of operation.
 27. The method of claim 26, wherein the secondvoltage source is a battery, and wherein the method further comprises:detecting an outage of the first voltage source; producing the positiveDC voltage and the negative DC voltage from a voltage of the battery ina backup mode of operation.
 28. The method of claim 27, furthercomprising producing an output AC voltage from the positive DC voltageand the negative DC voltage in both the line mode of operation and thebackup mode of operation.
 29. The method of claim 28, further comprisingisolating the first voltage source from the first node and the secondnode in the backup mode of operation.
 30. The method of claim 26,wherein the second voltage source includes a battery, and wherein themethod further includes charging the battery in the line mode ofoperation.
 31. The method of claim 26, further comprising simultaneouslydrawing current from both the first voltage source and the secondvoltage source in a combined mode of operation.
 32. The method of claim31, wherein the second voltage source is a battery.